A study of femoral artery by twin drivers in magnetic resonance interference elastography

Magnetic Resonance Elastography (MRE) is a phase-contrast technique using conventional Magnetic Resonance Imaging system to visualize propagating shear waves and study the stiffness of tissues. Usually, shear vibrations are applied to the surface of tissues by means of mechanical driver at one point. But in femoral artery study, the shear wave generated by the single driver on the surface of thigh cannot reach the femoral artery behind vein because of the blockage from the vein. In this study, the twin drivers set developed in our laboratory is used to overcome the problem. By using twin drivers driven simultaneously, interference shear wave pattern is generated. MR Interference Elastography is using interference shear wave image to study the stiffness of tissues. And, a finite element modeling was used to simulate single and twin driver datasets. The method was applied to in vivo human's femoral artery. And the result demonstrates the feasibility of this method. Further study will be conducted with the twin drivers in more in-vivo studies.

Relationship between antiphospholipid antibodies and progression of lower extremity arterial occlusive disease after lower extremity bypass operations

PURPOSE

Antiphospholipid antibodies (APLs), which consist of anticardiolipin antibodies (ACLs) or lupus anticoagulant (LA), are associated with venous thrombosis, stroke, and cardiac events. Although they are present in many patients with lower extremity atherosclerotic occlusive disease (LEAOD), the relationship between APL and the progression of LEAOD has not been reported. A comparison of progression of LEAOD as determined with direct imaging studies in patients with and without APL forms the basis for this report.

METHODS

APL+ patients (immunoglobulin M [IgM] or IgA or IgG ACL > 3 SD units above control mean or positive LA) who underwent lower extremity bypass grafting between January 1990 and June 1999 (n = 79) were compared with an APL control group (n = 68). Members of the study and control groups were similar with respect to age, procedure, sex, length of follow-up, and multiple atherosclerosis risk factors. Progression of LEAOD was determined by comparing preoperative arteriograms with postoperative imaging studies (arteriograms or duplex scanning). External iliac, common femoral, superficial femoral and popliteal arteries were graded as < 50% stenosis, > or = 50% stenosis, or occluded. Posterior tibial and anterior tibial arteries were graded as patent or occluded. Progression was defined as any increase in stenosis category.

RESULTS

The mean follow-up period was 31 months for APL+ and 35 months for APL- patients (P = not significant). Progression of LEAOD occurred in 58 (73%) of 79 APL+ patients and in 25 (37%) of 68 APL- patients (P <.001). There was no difference in progression in external iliac or common femoral arteries. Differences in progression were noted in more distal arteries; APL+ patients had significantly more progression in superficial femoral (45% vs 16%, P <.01), popliteal (31% vs 12%, P <.01), posterior tibial (29% vs 13%, P <.05), and anterior tibial arteries (29% vs 14%, P <.05). Multivariate logistic regression analysis showed a significant independent association between the presence of APL and progression of LEAOD (P <.0001).

CONCLUSION

In this study, the presence of APL in patients undergoing lower extremity bypass operations was a significant independent risk factor for progression of LEAOD. We conclude that this patient group should be closely monitored in the postoperative period and appears ideally suited for prospective studies of therapies to modify LEAOD progression.

Iterative statistical approach to blind image deconvolution

Image deblurring has long been modeled as a deconvolution problem. In the literature, the point-spread function (PSF) is often assumed to be known exactly. However, in practical situations such as image acquisition in cameras, we may have incomplete knowledge of the PSF. This deblurring problem is referred to as blind deconvolution. We employ a statistical point of view of the data and use a modified maximum a posteriori approach to identify the most probable object and blur given the observed image. To facilitate computation we use an iterative method, which is an extension of the traditional expectation-maximization method, instead of direct optimization. We derive separate formulas for the updates of the estimates in each iteration to enhance the deconvolution results, which are based on the specific nature of our a priori knowledge available about the object and the blur.

A mathematical analysis of the DCT coefficient distributions for images

Over the past two decades, there have been various studies on the distributions of the DCT coefficients for images. However, they have concentrated only on fitting the empirical data from some standard pictures with a variety of well-known statistical distributions, and then comparing their goodness of fit. The Laplacian distribution is the dominant choice balancing simplicity of the model and fidelity to the empirical data. Yet, to the best of our knowledge, there has been no mathematical justification as to what gives rise to this distribution. We offer a rigorous mathematical analysis using a doubly stochastic model of the images, which not only provides the theoretical explanations necessary, but also leads to insights about various other observations from the literature. This model also allows us to investigate how certain changes in the image statistics could affect the DCT coefficient distributions.

Discrete cosine transform domain restoration of defocused images

In discrete-cosine-transform-based (DCT-based) compressions such as JPEG it is a common practice to use the same quantization matrix for both encoding and decoding. However, this need not be the case, and the flexibility of designing different matrices for encoding and decoding allows us to perform image restoration in the DCT domain. This is especially useful when we have severe limitations on the computational power, for instance, with in-camera image manipulation for programmable digital cameras. We provide an algorithm that compensates partially for a defocus error in image acquisition, and experimental results show that the restored image is closer to the in-focus image than is the defocused image.

Inferior epigastric artery pseudoaneurysm: a complication of paracentesis

Two patients had inferior epigastric artery pseudoaneurysms after therapeutic paracentesis for ascites caused by portal hypertension. The first patient, a 62-year-old man, had a two-week history of left lower quadrant pain, tenderness, and nonpulsatile mass after a paracentesis for ascites. A left inferior epigastric artery pseudoaneurysm measuring 10 cm in diameter and 20 cm in length was diagnosed by means of Duplex ultrasound and arteriography. The patient was treated with percutaneous embolization, with successful thrombosis of the pseudoaneurysm. The second patient, a 33-year-old woman, had a six-week history of left lower quadrant pain, tenderness, and nonpulsatile mass after a paracentesis for ascites. Computerized tomography and arteriography showed a left inferior epigastric artery pseudoaneurysm, measuring 7 cm in diameter and 9 cm in length. The patient was treated with percutaneous embolization with successful thrombosis of the pseudoaneurysm. Both patients were discharged in good condition 2 days after embolization. Inferior epigastric artery pseudoaneurysm is a complication of paracentesis, and percutaneous embolization may be preferable to surgical repair in patients with chronic liver failure and portal hypertension.